There's been some talk recently about the use of carbon additives to reduce the effects of sulfation in renewable energy batteries. Sulfation can occur when batteries are operated in a partial state of charge (PSOC) application, common when batteries are charged with solar cells, wind turbines and other unpredictable power sources. Even though these systems regularly recharge the batteries, they don't always provide a sufficient level of overcharge. The effect of continual undercharge can, over time, cause "hard sulfate" crystals to form on both the positive and negative battery plates. These crystals can reduce the capacity of the battery and make it even more difficult to fully charge, resulting in short battery life.

Sulfation related to PSOC applications is a phenomenon that was first observed in electric vehicle and hybrid electric vehicle applications using sealed valve regulated lead acid batteries (VRLA). When AGM (or GEL) VRLA batteries are used in PSOC applications, the recombination process occurring at the negative plate disproportionately discharges the negatives in relation to the positives and creates an imbalance in their relative states of charge. Normally this imbalance is corrected by providing enough overcharge during normal charge, and/or providing an equalization charge, to bring them back into balance. In PSOC applications, the batteries are not overcharged or equalized enough to re-balance the state of charge, and the negative plates become severely sulfated.

Several battery research groups have found that by using various new types of carbon in the negative plates of VRLA batteries, the sulfation issue could be addressed. "These new carbons are often referred to as smart carbon, hyper carbon, ultra carbon, graphene or nano-carbon," says Fred Wehmeyer, Senior VP Engineering at U.S. Battery Manufacturing. "But they may or may not be composed of carbon nano-tubes that are still too expensive for large scale applications.”

The significance of this is that negative plate sulfation is a phenomenon that applies specifically to VRLA (AGM & GEL) batteries. Smart carbon technologies intended to address negative plate sulfation in VRLA batteries do nothing to address sulfation of the positive plates in a flooded deep cycle battery, which is the primary issue when these batteries are undercharged or used in PSOC applications.
U.S. Battery has developed a different approach to address sulfation using the company's exclusive Outside Positive (OSP™) plate battery design. The OSP™ plate construction is designed to balance the capacity of the positive plates versus the negative plates.

This balanced active material ratio allows the positive and negative plates to reach full charge at the same time, thus preventing sulfation of one plate versus the other. Most batteries with conventional OSN (outside negative) plate construction end up with an excess of negative active material. Adding "Smart Carbon" to the negatives does not address this active material imbalance problem. Balancing the active materials with OSP™ addresses the disparate sulfation problem in addition to the other benefits.

"The battery industry is continually looking for ways to improve the current technology. Sometimes the latest and greatest idea isn’t always the best for every application," says Don Wallace CMO Executive Vice President at U.S. Battery Manufacturing. "At the end of the day, you often find that new versions of old ideas are the most productive. Either way involves exhaustive testing to prove or disprove, and in the end, it will ultimately be the customer who makes the determination. It is our job to do the background work necessary to provide customers with the necessary data and quantifiable analysis so that they can make the most educated buying decision. This recent news about carbon has been touted as something that can drastically improve the overall performance of the flooded lead acid battery. But the facts should be completely understood before buying flooded batteries with a carbon additive when sold as a value added feature.”
For additional information on U.S. Battery's OSP™ battery design for Renewable Energy applications, visit www.usbattery.com.